The present invention relates to seat belt pretensioners and, more specifically, to a seat belt pretensioner that incorporates a motion multiplier thereby reducing the actuator stroke requirement.
Seat belt pretensioners remove slack from a seat belt in the event of a collision in order to minimize forward movement of the passenger. While it is known to use pyrotechnic gas generators to operate mechanisms which wind up or otherwise pull in slack in the seat belt during a collision, such known pyrotechnic gas generators are often disposed internally of a seat belt retractor. Thus, the vehicle owner is faced with a significant cost penalty in that the entire pretensioner and retractor assembly must be replaced after activation because of the inability to prevent degradation of the retractor. High-temperature gases tend to abrade interior metal surfaces and produce ash and clinkers that bind up the retraction mechanism.
Another problem with known pretensioners is that they are designed to activate only in severe accidents, for example, accidents that exhibit xe2x80x9cGxe2x80x9d forces sufficient to activate the vehicle airbags. Safety system designers generally choose such a relatively high activation threshold due to the expense of replacing the entire seat belt retractor and pretensioner assembly after activation. As a result, seat belt pretensioners do not protect passengers in less severe accidents.
A related problem with known pretensioners is that when the pretensioner is activated only in severe accidents, activation is relatively late in the crash sequence. Thus, the pretensioner must rapidly take up slack in the seat belt, sometimes injuring the passenger.
U.S. Pat. No. 5,967,440, herein incorporated by reference, describes a pretensioner and a conventional retractor for a safety belt system. When compared to the seatbelt retractor, the pretensioner is relatively complex and large, thus increasing the weight and spatial requirements of the seatbelt assembly.
U.S. Pat. No. 5,899,399, herein incorporated by reference, describes a state of the art pretensioner. The pretensioner is relatively complex therefore complicating the manufacturing process.
U.S. Pat. No. 5,944,350, herein incorporated by reference, describes a state of the art pretensioner. Again, the pretensioner is relatively large, thus increasing the weight and spatial requirements of the seatbelt assembly.
German Patent No. DE 10010379 A1, herein incorporated by reference, describes a pretensioner having an arcuate path for a multi-piece actuator (a plurality of cylinders) that drives a steel cord wrapped around a webbing reel hub and thereby effects pretensioning of an associated seat belt. The manufacturing of the pretensioner is more complex given the multi-piece actuator and given the arcuate channel that the actuator must traverse Uniformity in channel width and effective sealing becomes more difficult with the use of an arcuate channel. Secondly, a noise reduction means is employed to prevent rattling during normal vehicle operation, thereby increasing manufacturing costs. Furthermore, the joint use of the multi-piece actuator with the steel cord results in a friction loss and a reduction in the load applied to the steel cord by the forward-most cylinder of the actuator. As a result, more force is required to drive the multi-piece actuator and pretension the seatbelt. One solution is described by the use of an intermediate element xe2x80x9c43xe2x80x9d for facilitating the smooth movement of the rotating elements along the arcuate channel. Consequently, without the use of the intermediate element xe2x80x9c43xe2x80x9d, a more robust pretensioner housing would be necessitated to withstand the relatively greater combustion pressure (produced by a greater amount of propellant) likely necessary to pretension the seatbelt in accordance with customer requirements.
The aforesaid problems are solved, in accordance with a preferred constructed embodiment of the present invention, by a seat belt pretensioner that utilizes a flat strap as a motion multiplier and a linear channel for movement of a pretensioner actuator, thereby reducing the load or force lost to friction in certain known pretensioners. Given the ease of sealing, the present design also inhibits retractor and occupant exposure to the gases and solids formed upon combustion of a pyrotechnic composition contained within the pretensioner.
In one embodiment of the invention, the pretensioner contains a housing, a clutch assembly that in operation rotatably and constrictively communicates with a webbing reel shaft of a seatbelt retractor, a strap that constrictively exerts a circumferential pressure about the clutch assembly upon pretensioner activation, an actuator that communicates with and is propelled against the strap upon pretensioner activation, a gas generant or pyrotechnic that propels the actuator (or piston), and an initiator that ignites the gas generant upon a signal from an accelerometer or impact sensor, for example. Upon ignition of the gas producing pyrotechnic, the actuator is driven forward in an essentially linear path thereby tightening the strap about the clutch assembly, and thus pretensioning the seat belt wound about a spool in the retractor, wherein the spool and the clutch assembly share the webbing reel retractor shaft as an axis in a preferred embodiment.
Stated another way, a pretensioner 10 for a seat belt 12 utilizes a strap 34 coiled about a clutch assembly 46 wherein the clutch assembly 46 is in normal operation of a vehicle, rotatable about a portion of a webbing reel shaft 16. The pretensioner 10 contains a first passage 20 and a second passage 22 for the respective containment of the clutch assembly 46 and an actuator 32, wherein each passage is formed perpendicular and in volumetric intersection with the other. The pretensioner 10 also contains a gas generant composition 30 in combustive communication with the actuator 32. Upon ignition, the gas pressure produced by the pyrotechnic 30 propels the actuator 32 into the strap 34, thereby effecting rotary advancement of the clutch assembly 46 and the shaft 16, and thus pretensioning the seat belt 12 wound about a spool 13 of a seat belt retractor 14, wherein the spool 13 is rotatably engaged with a second portion of the shaft 16 and thus provided in coaxial relation with the clutch assembly 46.
After use, only the pretensioner and perhaps the retractor shaft need be replaced, obviating the expense of also replacing the retractor or other components of the seat belt retraction mechanism.
Because expense heretofore associated with activation of a pretensioner is significantly reduced, passengers can be given the protection of seat belt pretensioning in even minor accidents. Moreover, a pretensioner that activates in minor collisions will also activate earlier in a severe crash sequence. Earlier activation of the pretensioner permits the pretensioner to operate less aggressively, reducing the possibility of injury caused by the seat belt pretensioner itself.